Fractal Reflectarray Antennas: State of Art and New Opportunities

Abstract

Fractal geometries are appealing in all applications where miniaturization capabilities are required, ranging from antennas to frequency selective surfaces (FSS) design. Recently, some fractal patches configurations, giving low losses, reduced size, and quite good phase ranges, have been proposed for the design of reflectarray unit cells. This paper reviews existing fractal-based reflectarrays, highlighting their benefits and limitations. Furthermore, a comprehensive analysis of an innovative reflectarray unit cell, using a fractal-shaped fixed-size patch, is presented. The miniaturization capabilities of the Minkowski fractal shape are fully exploited to obtain a compact cell offering quite good phase agility, by leaving unchanged the patch size and acting only on the fractal scaling factor. Experimental validations are fully discussed on a realized 10 GHz0.3λ×0.3λcell. This is subsequently adopted to synthesize various reflectarray prototypes offering single or multiple-beam capabilities over a quite large angular region (up to 50 degrees). Finally, experimental validations on a realized15×15elements prototype are presented to demonstrate the wide angle beam-pointing capabilities as well as a quite large bandwidth of about 6%.

A Dual-Band Compact Metamaterial Absorber with Fractal Geometry

“…The above fractal configuration allows to host an electrically longer resonator into a smaller unit cell [18,19], thus offering very appealing miniaturization skills. As a matter of the fact, the combined use of a smaller patch length L and a greater S-value allows to move down the patch resonance frequency, f 0 .…”

Modified Minkowski Fractal Unit Cell for Reflectarrays with Low Sensitivity to Mutual Coupling Effects

“…To this end, a research routine is implemented that fits the desired ϕ nm values onto the simulated phase curves (Figures 5(a)-7(a)), finally returning the corresponding scaling factors S nm or the patch lengths L nm . A more detailed description of the implemented research routine is reported in [13]. Figure 11(e) illustrates the comparison between the radiated H plane patterns.…”

“…To this end, a modified layout of the fractal unit cell, originally introduced by the authors in [12,13], is investigated and discussed in this paper to increase the unit cell insensitivity to mutual coupling, thus preserving the effectiveness of the infinite array approach, even in the case of highly miniaturized reflectarray cells.…”

Miniaturization of a Microstrip Patch Antenna with a Koch Fractal Contour Using a Social Spider Algorithm to Optimize Shorting Post Position and Inset Feeding

“…Several techniques have been used in the miniaturization of microstrip patch antennas [7], such as material loading [8,9], shorting and folding [10][11][12][13][14], reshaping [15][16][17][18][19][20], modifying the ground plane [21,22], using metamaterials [23][24][25], and using fractal contours [26][27][28][29][30].…”